http://downloads.bbc.co.uk/writersroom/scripts/screenplay.pdf
From reading any script, whether for film, television, radio or stage, there are three fundamental principles:
1. The basic elements of a script are:
- actions,
- dialogue,
- speakers’ names.
2. All three of these are typed and laid out distinctively — so it’s easy to tell them apart.
3. Actions are written in the present tense (‘Alice goes to Bill’, not ‘Alice went to Bill’).
I have learnt that most on the script will be made up of: Sluglines, Action, Character Names, and Dialogue.
1) Sluglines, also known as Scene Headings. These appear at the beginning of a new scene and tell us the scene's setting. They look like this:
INT. BANK VAULT - NIGHT
Or this:
EXT. FOOTBALL STADIUM - LATE AFTERNOON
Sluglines are made up of these three elements:
Sometimes, you'll need a Sublocation to clarify the Location. That looks like this:
INT. DONALD'S MANSION - BILLIARDS ROOM - NIGHT,
a new scene occurs every time there's a shift in Time, Location, or both.
2) Action. This describes what is happening on the screen, and which characters (if any) are involved. It looks like this:
INT. DONALD'S MANSION - BILLIARDS ROOM - NIGHT
Alice picks her way through the ransacked room. Cue sticks, books, papers—everything has been searched. She stoops to pick up a photo of a dog.
With a few exceptions the Action follows standard rules of capitalization. It's single-spaced and always in present tense. (If the action happened in the past, the Slugline will tell us this.)
Also, you always need some Action after a Slugline, even it's only a single line. Like this:
EXT. RITZ-CARLTON - DAY
The stretch limousine bursts into flames.
3) Character Name. This always appears above Dialogue and tells us which character is speaking.
Character names are always in ALL CAPS.
And sometimes there are minor characters that you won't need to name you can call them anything you want like Zombie or Survivor or Monkey Butler. If there are several of the same type of character, add a number: COP #1 or BODY BUILDER #2.
4) Dialogue. The words the character speaks. It looks like this:

or this:

Dialogue is single-spaced and follows standard rules of capitalization. Unlike in novels, there are no quotes around Dialogue, unless the character is quoting someone.
Now, here's an example of how all four elements come together on the page:

CUTS:
It used t be standard to use the words "CUT TO:" to indicate a change in scene. Nowadays, the cut that comes with a scene change is implied by a new Slugline and CUT TO isn't used as much.
The best time to use CUT TO is when you really want to emphasize the shift between two scenes.
You can use Jump cut or Smash cut to imply a super-fast, in-your-face editing style. No matter how it's written, a cut always happens in 1/24th of a second - the amount of time it takes to switch from one frame to the next.
FONT, MARGINS, AND SPACING
Screenplays live on letter-sized paper (8.5 x 11 inches). They're always written in Courier font, 12 point, 10 pitch. No bold, no italics.
Page Margins:
Left: 1.5 inches
Right: 1 inch
Top: 1 inch
Bottom: 1 inch
Screenplay Element Margins
I have learnt that most on the script will be made up of: Sluglines, Action, Character Names, and Dialogue.
1) Sluglines, also known as Scene Headings. These appear at the beginning of a new scene and tell us the scene's setting. They look like this:
INT. BANK VAULT - NIGHT
Or this:
EXT. FOOTBALL STADIUM - LATE AFTERNOON
Sluglines are made up of these three elements:
- 1) INT. or EXT. Short for Interior and Exterior, this tells the production crew whether or not they'll be shooting on a sound stage or on location.
- 2) Location. Where the scene takes place. These should be short: Shed or Car Park or Jo's Bedroom.
- 3) Time. Usually just Day or Night but can be as specific.
Sometimes, you'll need a Sublocation to clarify the Location. That looks like this:
INT. DONALD'S MANSION - BILLIARDS ROOM - NIGHT,
a new scene occurs every time there's a shift in Time, Location, or both.
2) Action. This describes what is happening on the screen, and which characters (if any) are involved. It looks like this:
INT. DONALD'S MANSION - BILLIARDS ROOM - NIGHT
Alice picks her way through the ransacked room. Cue sticks, books, papers—everything has been searched. She stoops to pick up a photo of a dog.
With a few exceptions the Action follows standard rules of capitalization. It's single-spaced and always in present tense. (If the action happened in the past, the Slugline will tell us this.)
Also, you always need some Action after a Slugline, even it's only a single line. Like this:
EXT. RITZ-CARLTON - DAY
The stretch limousine bursts into flames.
3) Character Name. This always appears above Dialogue and tells us which character is speaking.
Character names are always in ALL CAPS.
And sometimes there are minor characters that you won't need to name you can call them anything you want like Zombie or Survivor or Monkey Butler. If there are several of the same type of character, add a number: COP #1 or BODY BUILDER #2.
4) Dialogue. The words the character speaks. It looks like this:

or this:
Dialogue is single-spaced and follows standard rules of capitalization. Unlike in novels, there are no quotes around Dialogue, unless the character is quoting someone.
Now, here's an example of how all four elements come together on the page:

CUTS:
It used t be standard to use the words "CUT TO:" to indicate a change in scene. Nowadays, the cut that comes with a scene change is implied by a new Slugline and CUT TO isn't used as much.
The best time to use CUT TO is when you really want to emphasize the shift between two scenes.
You can use Jump cut or Smash cut to imply a super-fast, in-your-face editing style. No matter how it's written, a cut always happens in 1/24th of a second - the amount of time it takes to switch from one frame to the next.
FONT, MARGINS, AND SPACING
Screenplays live on letter-sized paper (8.5 x 11 inches). They're always written in Courier font, 12 point, 10 pitch. No bold, no italics.
Page Margins:
Left: 1.5 inches
Right: 1 inch
Top: 1 inch
Bottom: 1 inch
Screenplay Element Margins
- Slugline: left margin 1.5 inches
- Action: left margin 1.5 inches
- Character name: left margin 3.7 inches
- Dialog: left margin 2.5 inches, right margin 2.5 inches (or 6 inches from left edge of page)
- Parentheticals: left margin 3.1 inches, right margin 2.9 inches
- Between Slugline and Action: double space
- Between Action and more Action: double space
- Between Action and Character Name: double space
- Between Character Name and Dialogue: single space
- Between Dialogue and the next Character Name: double space
- Between Dialogue and Action: double space
- Between Character Name and Parentheticals: single space
- Between Parentheticals and Dialogue: single space
- Between Action and Slugline: double space
- Between Dialogue and Slugline: double space